NEW YORK (Reuters Health), Dec 30 - Tests show that certain MRI machines may demagnetize magnets used in cochlear implants to couple external and implanted components, according to a report in the December issue of Otolaryngology--Head and Neck Surgery.
"Cochlear implants contain internal magnets used to transcutaneously couple the externally worn processor to the surgically implanted components," Dr. Omid Majdani, of the Medical University of Hannover, Germany, and colleagues write. These magnets, they note, interact with other magnets such as those found in MRI scanners, and that the dynamic magnetic fields may induce voltages or temperatures that could harm the implant or the patient.
The researchers examined the level of demagnetization of the magnets and temperature changes in cochlear implants in a 3.0-tesla (3.0T) MRI.
They found that demagnetization of the cochlear implant magnets is dependent of the angle between the magnetic field of the magnet and the MRI. When the angle between the MRI magnet and the CI magnet was greater than 80°, demagnetization reached unacceptable levels.
"Although little to no demagnetization occurred if the angle between the poles of the CI magnet and MRI magnet was up to 80°, identification of magnetic poles is not uniform between patients or scanners," Dr. Majdani's team explains. "Extensive procedural changes would be necessary to ensure that a safe orientation was maintained before 3.0T MRI scanning with such implants could be advocated."
The maximum temperature increase in the cochlear implants was 0.5° C, within the acceptable limit of 1.0° in any location.
Otolaryngol Head Neck Surg 2008;139:833-839.
Last Updated: 2008-12-29 11:25:41 -0400 (Reuters Health)
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